The difficulty of decoding a 21-character password depends on several factors, including the complexity of the password, the encryption or hashing algorithm used to secure it, and the resources available to the hacker. Let’s examine these factors:

1. Password Complexity: A 21-character password can range from extremely secure to relatively vulnerable, depending on its composition. A password that uses a mix of uppercase and lowercase letters, numbers, and special characters is significantly harder to crack than one composed of simple, predictable patterns or repeated characters.
2. Encryption or Hashing Algorithm: If the password is stored or transmitted in a secure manner using a strong, up-to-date encryption or hashing algorithm, it will be much harder for a hacker to decode. Older or compromised algorithms might provide easier targets for hackers.
3. Hacking Resources and Techniques: The time and resources required to decode a password can vary dramatically. A brute force attack, where every possible combination is tested, would take an impractical amount of time for a 21-character mixed-use password due to the astronomical number of possible combinations. However, more sophisticated attacks, like those using dictionary attacks, pattern checking, or exploiting system vulnerabilities, might reduce the required time, especially if the password is not complex.
4. Computational Power: The speed of password cracking has increased with advancements in technology. The use of powerful computers or networks of computers (including the use of specialized hardware like GPUs or more illicit botnets) can significantly reduce the time needed to break a password.

To provide a rough estimate of the difficulty, let’s calculate the number of possible combinations for a 21-character password, assuming different levels of complexity (e.g., alphanumeric with and without special characters). Let’s calculate:

For a 21-character password, the number of possible combinations is as follows:

• For alphanumeric characters only (uppercase and lowercase letters plus numbers): approximately 4.37×10394.37×1039.
• Including special characters: approximately 2.73×10442.73×1044.

These numbers represent the total possible combinations a brute force attack would need to explore to guarantee finding the correct password. Given these astronomical numbers, even with powerful computing resources, decoding a 21-character password through brute force would be extremely challenging and time-consuming.

The actual time to crack the password would depend on the attacker’s computing power. For a strong, random 21-character password, the odds of a hacker successfully decoding it quickly are exceedingly low, especially if secure hashing and encryption methods protect the password. However, it’s important to note that no system is entirely impervious to hacking, especially if other vulnerabilities can be exploited.